1. Field of Invention
The invention relates to immunoassay test devices and more particularly to a test device having a stopping mechanism adapted to freeze a test result at a stopping time so as to keep the test result as a permanent record and enable the qualitative tests to become quantitative or semi-quantitative tests.
2. Description of Related Art
Interruption of chemical, biochemical, or immunological reaction requires the removal and/or separation of reactants, intermediates, products, or reaction mediums from the reaction mixture, or changes of the temperature, reactants, or physical parameter of the reaction mixture. The interruption procedures usually demand tedious manipulations and extra time. Therefore, most rapid tests produce qualitative results only rather than produce quantitative or semi-quantitative test results. Undoubtedly, a simple, easy, rapid, and inexpensive method to terminate the reaction in situ will be useful to all users.
There have been numerous suggestions in prior patents for lateral flow chromatographic immunoassay methods and devices. For example, U.S. Pat. No. 4,956,302 to Gordon and Pugh; WO 90/06511 to H. Buck, et al; U.S. Pat. No. 6,764,825 to T. Wang; U.S. Pat. No. 5,008,080 to W. Brown, et al; and U.S. Pat. No. 6,183,972 to Kuo and Meritt. This technique has been commercialized for the productions of easy-to-use rapid diagnostic tests, such as Clearblue One-Step Pregnancy Test in 1988 (EP 291194; EP 560411). The One-Step Immunodiagnostic Test can show qualitative result rapidly. However, it cannot provide quantitative or semi-quantitative result because, among other reasons, there is no mechanism to terminate the reaction at a fixed time. Hence the intensity of the result signal varies continuously with time.
Qualitative test provides yes or no (i.e., positive or negative) data to the presence of the antigen (the analyte to be detected) in the sample solution, whereas quantitative or semi-quantitative test provides the data of the amount or the level of the amount of the antigen in the sample, which are more informative and important to the test users. For example, a positive drug of abuse test result has no legal meaning unless the amount of drug exceeds the legal limit. Also, there is always a background level of Luteinizing Hormone (LH) in the woman's body fluids. When the LH level has surged to a certain level the ovulation will then occur in 1-2 days (K. Elkind-Hirsch, et al, Obstetric and Gynecology, 67 (3):4450, 1986). Therefore, qualitative test cannot provide any useful information for LH diagnosis, because both the background and the surged levels of body fluid samples will give the same positive results. Detection of the Prostate Specific Antigen (PSA) levels at 4 ng/ml or less has no diagnostic significance, even though a positive result is shown in a qualitative test. The PSA levels higher than 4 ng/ml have different etiological significance (H. Rittenhouse, et al, Critical Rev. in Clin. Lab. Sci., 35(4):275, 1998; W. Catalona, et al, J. Am. Med. Asso., 274(15):1214, 1995). The C-Reactive Protein (CRP) levels reflect the kind and severity of different symptoms (L. Powell, Am. J. Med. Technol., 87:138, 1979; N. Rifai and P. Ridkeer, Clin. Chem., 47:28, 2001; P. Ridker, et al, Circulation, 97:425, 1998). Qualitative tests cannot differentiate the levels of the antigen amounts and provide early warning signals and information. The levels of Human Chorionic Gonadotropin (HCG) can provide useful information for the detection and the monitoring of pregnancy, ectopic pregnancy, threatened abortion, or selected malignancies of trophoblastic and non-trophoblastic origin (R. Frances and M. Batzer, Fertil. Steril., 34:1, 1980; M. Dhont, et al, Lancet, i:559, 1978; N. Kadar and R. Romero, Lancet, i:1205, 1981; P. Jouppila, et al, Br. J. Obstet. Gynecol., 86:343, 1979; H. Bates, Lab. Manag., 18:25, 1980; M. Dawood, et al, Obstet. Gynecol., 50:172, 1977; P. Papepetrou, et al, Cancer, 45:2583, 1980). Clearly, while keeping the advantages of low cost, quickness, simplicity, and versatility of the well known One-Step Immunodiagnostic Test, endowing it with semi-quantitative or quantitative detection capacity will be extremely useful and popular in the field of medical diagnostics and diagnostic testing in general.
Thus, it is desirable to provide a novel stoppable test device having a stopping mechanism for the One-Step Test, as well as for other tests and reactions, so that quantitative or semi-quantitative data can be obtained rapidly and easily with a simple test device.